I studied the VNT controller in a VW with AFN engine.
Basically the vanes are open for low back pressure and low EGT.
Once the driver pushes the pedal the controller "knows" the desired boost, depending on throttle position. Each throttle position has its desired boost level.
Again, the driver pushes the pedal, immediately the vanes close to max. closed position, boost rises until desired boost is reached. Fast start up, slow approach to avoid over peak. I think this is called PID behaviour.
If the pedal is released after hard acceleration the vanes open as pedal position is zero.
In reality the desired boost is set higher at idle (pedal position = zero) than the turbo can do at that time. The vanes are rather closed trying to build up boost but can't as not enough rpm. This gives fast response and it does not matter to have closed vanes at idle. Coming from high rpm after hard acceleration the vanes have to decrease boost and open completely until boost is down.

The VW ECU has many more input like air mass flow and all including the engine management is integrated in one unit.

In my opinion the most attractive way to do a stand alone unit is with Arduino (because of the PWM output for the N75).

Tom